The instant invention relates generally to machinery seals disposed in grooves or seal glands to provide a fluid seal between relatively moving machinery parts. Specifically, the invention comprises a pair of annular seal elements arranged in an inverted nesting relationship each having an axial slot therein and an axial key portion extending therefrom. An annular support element is disposed radially inwardly of the nesting annular seal elements to provide radial force on the nesting seal elements thereby enhancing the sealing characteristics of the assembly.
Hydraulic fluid sealing applications often require robust double-acting seal assemblies for pistons or rods, or any axially displaceable machine part moveable through an annular passage in a complementary part. These seal assemblies provide a fluid barrier between reciprocating piston rods or pistons and a fluid under pressure by means of a dynamic sealing element that provides radial force against a rod shaft or a piston wall, thereby preventing fluid flow from an area of high pressure to an area of low pressure.
In high pressure fluid system applications, for example heavy machinery hydraulic systems, it is well known in the art to use seal assemblies such as xe2x80x9cTxe2x80x9d seals, capped xe2x80x9cTxe2x80x9d seals, glide ring piston seals, or thermoplastic sealing rings employing step joints arranged in series along the axis of a shaft or piston to prevent high pressure fluid from leaking past the seals. The upstream seals in these multi-seal arrangements, known as buffer seals, serve to protect the primary rod or piston seal from high-pressure surges, thereby extending the useful life thereof.
However, the aforementioned conventional seal assemblies suffer from several disadvantages. xe2x80x9cTxe2x80x9d seals typically comprise a soft dynamic sealing element nested with a pair of back-up rings disposed in a seal gland. The soft sealing element, while providing excellent non-dynamic sealing properties (very little drift), nonetheless is subject to wear and proves unable to bridge small ports because of its tendency to extrude into a port when under pressure.
Capped xe2x80x9cTxe2x80x9d seals, more robust than xe2x80x9cTxe2x80x9d seals, are typically comprised of a PTFE material cap, an elastomeric energizer, and a pair of anti-extrusion rings. The PTFE element reduces the tendency of the seal to wear over time but is expensive and difficult to install because it must be stretched into place. Additionally, the PTFE element is too soft to bridge small ports and can trap and hold contaminants that cause cylinder bore scoring.
The glide ring piston seal also has a PTFE dynamic sealing element employed in conjunction with an elastomer o-ring to provide radial sealing force. This seal assembly has excellent resistance to drift, but the PTFE sealing element cannot bridge small ports and is subject to damage from contaminants in the fluid system. The glide ring piston seal is also difficult to install in a seal gland and is subject to cutting and chipping upon installation.
Other known-in-the-art piston seal assemblies employ advanced thermoplastic materials to provide rigid dynamic sealing elements that have exceptional port-bridging abilities and relatively long-life. Unfortunately, rigid dynamic sealing elements require a great deal of force to install, and are therefore vulnerable to installation damage. Additionally, the less flexible dynamic sealing elements require strict attention to manufacturing tolerances to obtain an accurate fit in the piston gland, thereby increasing unit cost.
The instant invention solves the aforementioned problems by providing a seal assembly for a seal gland or groove having a pair of spaced axial walls and a radial wall in a relatively displaceable machine part. The seal assembly is comprised of a pair of identical annular seal elements arranged in an inverted nesting relationship disposed within the groove in proximity to the displaceable machine part to be sealed. The seal elements are made of a relatively hard, high strength plastic material resistant to wear from frictional forces, for example nylon. A resilient annular support element comprised of an elastomer is disposed between the sealing elements and the radial wall of the seal gland to provide radial sealing force against the relatively displaceable machine part, thereby preventing the flow of fluid between the seal elements and the machine part.
The annular seal elements each have an axial slot therein, bounded by a pair of beveled end surfaces tapered from the exterior radius thereof to the interior radius thereof that prevent extrusion of the resilient support element into the axial slot. Each seal element further has a key portion extending axially therefrom, disposed 180 degrees away from the axial slot around the circumference of the annular sealing element. The key portion has tapered axial surfaces thereon that are shaped to engage the tapered surfaces of the axial slot of an inverted seal element, thereby providing a pair of inverted nesting elements.
The key portion of the annular seal elements has an axial dimension slightly smaller than the axial dimension of the complementary axial slot in the opposing element. This feature of the instant invention causes the seal element oriented in the upstream (high pressure) direction to be forced by system pressure against the complementary element thereby sealing the axial mating surfaces thereof and preventing fluid flow between the nesting seal elements.
Optimum operation of the seal assembly obtains when the axial width of the pair of inverted, nesting seal elements is slightly less than the distance between the axial walls of the seal gland. This feature of the instant invention allows the seal elements to float in the gland while maintaining each element in close proximity to it""s complement such that a reverse in pressure direction rapidly forces the elements together to maintain a leak-proof seal.
The annular support element has an axial dimension less than the axial width of the pair of inverted nesting seal elements. This feature of the present invention allows for thermal expansion of the assembly in the seal gland and prevents, for example, the expansion of the assembly to a point where friction between the seal elements and the relatively displaceable part causes additional thermal expansion, eventually resulting in catastrophic seal failure. Since the axial width of the support element is less than that of the seal elements, upon a change in pressure from one side of the seal assembly to another, the seal elements will be forced to the downstream axial wall of the seal gland in advance of the support element, thereby preventing the more resilient support element from extruding out of the seal gland. This axial motion of the support element also acts to force the nesting seal elements together, thereby maintaining a tight pressure seal.
The tapered surfaces of the axial slot in the seal elements closely engage the key portion of the complementary element, thereby prohibiting the more resilient support element from being forced into the axial slot when under pressure. The support element provides radial force on the seal elements, biasing the tapered surfaces thereof towards the key portion of the complementary element. This radial force prevents both leakage and extrusion of the support element into the small space where each slot and its complementary key portion engage.
Therefore one object of the instant invention is a seal assembly having a pair of identical nesting annular seal elements made from a high strength, relatively hard plastic material to provide exceptional resistance to wear.
A further object of the instant invention is a seal assembly having a pair of seal elements each having an axial slot therein and a complementary axial key portion thereon such that, when inverted, the axial slot engages the key portion of the complementary seal element.
A yet further object of the invention is to provide a seal assembly having a support element that ensures that the assembly retains proper orientation in the seal groove throughout the useful life thereof.
A yet further object of the instant invention is a seal assembly that is not subject to chipping or cutting upon installation.
A yet further object of the instant invention is a seal assembly having a pair of identical nesting seal elements comprised of a high strength, relatively hard plastic material that are capable of bridging small ports in relatively moving machine parts.
A yet further object of the instant invention is a seal assembly having extremely low drift characteristics.
Additional objects, features, and advantages of the present invention will become apparent from the subsequent detailed description, taken in conjunction with the accompanying drawing figures.